One of the known techniques for replacing a heart valve in a human patient is to use a valve harvested from another mammal. Although the invention will be described for the most part with reference to replacing a patient's aortic valve (i.e., the valve between the left ventricle and the aorta), the principles of the invention can be adapted to other heart valve replacement procedures. Similarly, although heart valves harvested from pigs (porcine heart valves) are generally used, valves harvested from other mammals are possible alternatives.
In a known technique, a heart valve is harvested intact from a pig and treated to preserve it. (All references herein to such heart valves will be understood to include the immediately adjacent tissue, so that the structure thus referred to is an intact tube of tissue with the valve leaflets inside.) A so-called “stentless valve” is constructed by stitching a sleeve of fabric substantially concentrically around the outside of the harvested and preserved valve tissue. The resulting composite structure is sutured into the patient at the location from which the patient's natural valve leaflets have been removed. Two annular suture lines are typically employed. (Terms like “annular” and “annulus” are used herein solely as geometrical terms, and not to refer to any anatomical location or structure.) One suture line is located annularly around the valve adjacent the blood inflow (“proximal”) end. The other suture line is located annularly around the valve adjacent the blood outflow (“distal”) end. These two suture lines are generally regarded as necessary to ensure that there is no leakage of blood around the valve. The outflow suture line is also generally regarded as necessary to pin the commissure posts of the valve back (i.e., radially outward) against the root of the patient's aorta. The commissure posts of the valve are typically relatively long and flexible, and if they are not pinned back, they can fold over onto the valve leaflets in an undesirable way (e.g., impacting the leaflets and causing unnecessary wear). Over time (after implantation) the patient's natural body tissue is believed to advantageously grow into the fabric sleeve around the other material of the valve (i.e., the harvested and preserved valve tissue).
The high degree of flexibility of stentless valves of the type described above is believed to be beneficial to the patient. Such valves may compare favorably to the more rigid valves known as “stented” valves in respects such as the following: The rigidity of stented valves may stress the leaflets in the valve, which can cause tearing or calcification of the leaflets, which in turn can shorten the life of a stented valve. However, the stentless valves described above are thought by some to be somewhat more difficult to implant than stented valves or mechanical valves. As has been mentioned, stentless valves typically require two annular suture lines, whereas stented valves typically require only one annular suture line near the proximal end (because of the considerable stiffness imparted to the valve by the stent (typically metal) that forms part of the valve structure). Also, the high degree of flexibility of stentless valves can allow the commissure posts of the valve to fold down in the surgeon's way during placement of the first (inflow) suture line, and/or to permit one or more of those posts to be slightly mislocated when the final (outflow) suture line is made, with the possible result that the finally implanted valve may not close as completely and perfectly as it otherwise would.
In view of the foregoing, it is an object of this invention to improve heart valves of the stentless type described above.
It is another object of the invention to provide stentless heart valves that are more easily and more reliably implanted.